Resonance tuning indicator system



Dec. 12, 1939. F. B. sToNE RESONANCE TUNING INDICATOR SYSTEM Filed March 28, 1956 Ebb .WSW

Patented Dec. l2, 1939 fr'plurali .STATES PATENT cerros n e 2,183,206 RESONANCE TUNING INDICATOR SYSlEM` Frcd'B. Stone, Haddon Heights, N. J., assigner Y to Radio Corporation of America,

tion of. lDelaware a. corpcra- Application March 2s, 1936, serial No. '11,374 1o claims. (01.' 25o-20) The present invention relates to resonance tuning indicator systems, and more particularly, to

a system of that character for use'` in connection with a superheterodyne receiver having auto- Ilk matic volume control means. l

As iswell known', it is ydesirable to provide auto--y '15.: indicaton .system in connection with automatic volume control means ywhereby the resonance indication may be relatively sharp in its response to tuning-'adjustment While the automatic volume control function maybe independent `thereof and 20: relatively broad in its` response to the same tuning adjustment. I f n In a preferred embodiment oi the invention, a superheterodyne receiver is provided with radio frequencyfand intermediate frequency amplifiers, 25 and first' and secondfdetectors. The resonance tuned 'signal amplifying channel, while the automatic voiume' control means is applied to a more broadly tuned signal amplifying channel.

Itis, therefore, a further object of the present invention to provide a `resonance tuning indicatorsystem for radio receiving apparatus and the like, which includes a separate amplifying chan nel vfrom the signal .or modulated carrierwave 35 amplifying channel, for the automatic volume control means, and tof provide differing degrees of` selectivityin the two `channels. 1 They invention is particularly adapted for use in connection with an indicating device known on 40 the commercial market as an RCA 6E5 tube or Magic liye"` rlliis is a cathode ray devicel operated bya" control grid andhaving anelectrode associated with theta'rget'or fluorescent screen electrode'for casting a shadow thereon; the `width 45 of which varies with the potential applied to the electrode under control of the control grid.'

It is, therefore, a further object of the inventionto, provide an improved resonance tuning inicator system wherein a tuning indicator tube of the above type is used and to provide an improved coupling Acircuit therefor whereby it may be applied to a sharply tuned circuitsuch as the output circuit of `a vdiode second detector of a 55 superheterlodyne` receiver without effectingv the signal output characteristic of the. detector to cause distortion of demodulated signals,A

The invention will, however, be better understood from the following description when con- 6o sideredin Aconnection with the accompanying a portion of ythe circuit or tuning indication is applied to a more sharplyv drawing, and its scope will be-pointed outin the` appended claims.- i

In the drawing, Fig. 1 isa schematic circuit diagram ofl a radio receiving system provided with a resonance tuningindicator system and automatic voumecontrol means embodyingthe in. vention, and n l Fig. 2 is a similar schematic circuit diagram of of Fig. `1 showing a modification thereof.

Referring to Fig. l, the lradio receiving system.

shown is of thesuperheterodynetype comprising a radio frequency amplier tube 5 'coupled toa signal input circuit 5, such as an antenna circuit, through an input coupling transformer i tuned by a variable capacitor 8 vand supplying amplified signals through a second coupling transformer 9 to afrequency convertingdevice lo, ythe oscillator circuits ofwhich are notlshown for the purpose of simplifying the drawing. The transformer B is .tuned bya secondvvariable capacitor ll'c'on-v f .nected with the tuning controlrneans l2 for gang control with the capacitor 8. The oscillator tuningl capacitorand circuit. are not shown for rea-r sons as statedabove. l l.

'I 'he,-frequency converting device It is 'coupled through a rstg. intermediate lfrequencyI transe former i3' with an intermediate frequencyam- Apliflerztube Iii, the input circuit of -the amplier i4 being indicated aty I5. Automatic volume control potentials*for-.controlling.the tubes '5,' I@ and lil are appliedthereto through a lead' it andsuitable lters comprising series resistors i'l and by'- pass capacitors, i8.- Eachof `the tubes is also pro'- vided with suitable source of xed biasingf-poten- 1' tial for normallybiasing the tubes in the absencev of signals, and indicated in the present example,

by the self bias resistors lil.v

Circuit returns lare i made to thefchassis or ground asindicated bythe y.

ground connections 2i?. The'usual sup'erhetero-- dyne type of receiver is well known and understood and, accordingly, further description is bel,

lieved to be unnecessary, e l

The second detector-.is preferably of the diode type as indicated by the tube 2| and is provided withlananode'22 and aA cathode 23,01" the `:in-

directly heated type. The detector is connected with afrelatively sharply tuned input circuit 24 comprising r.the secondary 25 of an intermediate frequencycoupling transformer 2t and a shunt.

tuning capacitor` 2l. vThe yprimarylv of the transformer is connected in the plate circuitZB of the intermediate frequency amplier It in series with a limiting resistor 30 inthe anode potential supply-lead'l. n

The 'detectoror diode circuit include-sha Vseries filter resistor 32. and, a diode loutput'resistor 33 connected between the low potential side of the tuning input circuit 2li and ground 2t, to which is also connected thecathode 21"@y as indicated the lead 34. The anode 22 is connected to the high potential side of the tuned input circuit Z4.

Signals, such as a modulated carrier wave, received in response to the tuning adjustment of the tuning means I2, are rectified by the diode rectifier and the direct current and modulation components thereof appear across the output resistor 33. The resistor section 32 and a by-pass capacitor 35 to the cathode provide a filter for the intermediate frequency signals, whereby only the modulation or audio frequency component and the direct current or rectified portion of the signal appear across the output resistor section 33.

The modulation or audio frequency component of the signal is applied to an audio frequency amplifier tube 35 through a shielded lead con* nection 3'! with the high potential end 38 of the resistor 33 and, since the cathode 39 of the amplifier is connected to ground, as indicated, the amplifier 36 is also biased by the direct current potential existing in the resistor 33 in response to signals.

The audio frequency amplifier may be coupled to any suitable output circuit such as a lead 4D through an output circuit 4I coupled thereto through an output coupling choke coil 42 and an output volume control potentiometer 43. A limiting series resistor 44 adjacent to the anode 45 of the audio frequency amplifier 46 and a suitable by-pass capacitor 45 provide a further filter for the intermediate frequency signals. The output potentiometer i3 and the output anode choke coil 42 may be coupled directly or through a coupling capacitor indicated at 45.

The above described circuit arrangement provides a relatively sharply tuned intermediate frequency coupling circuit between the intermediate frequency amplifier and the second detector, whereby the response characteristic of the receiver may be sufficient to provide a desired degree of selectivity for the reception of signals in closely spaced signal channels without reducing the fidelity of response appreciably. This fidelity of response is materially enhanced by the direct coupling of the audio frequency amplifier with the diode output resistor in such a manner that the audio frequency amplifier device is biased by the rectified signal current and receives the audio frequency component directly without the intermediary of coupling means. To this end, the audio frequency volume control is placed in a circuit succeeding the first audio frequency amplifier, as shown, thereby loading the audio frequency or diode output resistor only with the grid of the amplifier tube 36.

To provide a broader tuning response for the automatic volume control means,l the same is provided with a separate signal amplifier channel from the amplifier channel for the second detector and, in the present example, comprises a second diode rectifier device having anodeelectrode 5i and a cathode 52 of the indirectly heated type connected with a relatively broadly tuned input circuit 53 comprising the secondary 55 of an intermediate frequency coupling transformer 55, the primary 56 of which is connected in the output circuit 5'I of an intermediate frequency amplifier tube 58, similar to the amplier tube I5, and this, in turn, is coupled with a coupling resistor 59 and a coupling capacitor Gli, in a circuit EI connected with a point 62 on the main signal channel preceding the sharply tuned circuit for the diode detector and, in the present example. a connection with the input circuit I5 of the last intermediate frequency amplifier I4.

It will be noted that the primary and second ary windings 55 and 54 of the transformer 55 for the automatic volume control diode 50 are not vtuned by shunt capacitor means but are made broadly resonant to the intermediate frequency, whereby the automatic volume control diode may receive and rectify a signal slightly in advance of or succeeding the exact resonance adjustment of the tuning means I2 for any received signal. Interference between adjacent signal channels is, thereby, reduced by the response of the automatic volume control means over a wider band than the detector.

The automatic volume control diode is provided with an output resistor 53 connected through ground 2Q with the cathode 52 and with the input circuit 53. Automatic volume control potentials are 'applied to the automatic volume control lead through an output connection 64 and a filter resistor 55 provided with a bypass capacitor 65 at the output end thereof in connection with the lead I6. q

The direction of flow of current in the diode output resistor G3 is of the polarity indicated to cause the rectified signal to increase the bias potential on the grids of the tubes 5, I0 and I4 to reduce the amplification and, thereby, control the gain. The increase in biasing potential is such that the initial potential derived from the self-bias resistors I5 is increased by the amount of the bias potential generated in the output resistor 63.

From the foregoing description it will be seen that the diode detector 2I is provided with a relatively sharply tuned signal amplifying channel including the amplifier device I4 and the tuned coupling transformer 26, While the automatic volume control diode 50 is provided with a separate, relatively broadly tuned, signal amplifying channel, including the substantially untuned coupling transformer 55 for the separate amplier device 58 coupled in parallel with the input circuit I5 of the amplifying channel for the detector.

This arrangement permits a desirable functioning of both the detector 'and the automatic volume control means in the presence of received signals and further permits the use of a tuning indicator in connection with the detector circuit from which may be derived a sharp tuning indication.

If such tuning indication vbe derived from the automatic volume control circuit in combination with the second detector circuit, it may not be made sufficiently broad for automatic volume control purposes without providing a relatively broad tuning response or relatively broad detector response.

In the present system, furthermore, the consideration of high audio frequency fidelity is important and this involves a relatively light or substantially zero load across the detector output resistor 33 and is accomplished by connecting the control grid 'I0 of a tuning indicator tube 'II through a shielded input lead 12 with the detector diode output resistor 33 at a suitable voltage tap point such as the point 38.

In a series with the lead 'l2 adjacent to the tap point is provided a relatively high resistance series path comprising a high resistance element i3, the output or grid end of which is bypassed to ground or chassis through an audio frequency bypass capacitor M. The resistor 'I3 is preferably of several megohms resistance, whereby the diode output resistor 33 is substantially unloaded, and

vsistor 3 3 of the 16 'for the Furthermore, the constants of the circuits` lshould besuch that the operation of the diode' the byepass capacitor 'i4 on the grid end 'of said resistoris of'suiiicient capacity to prevent audio frequency vsignals rfromreaching the grid 10 of the tuning indicatorv tube ll. Y f

In the present example, the-cathode l5v of vthe tuningindicator tube is connected tov the shield circuit of the receiven'whereby theiincreasedrectitled potential appearing across theoutput resharply tuned diode is applied between the control grid and the cathode to'cause the tuning indication to change in response to a received signal when tuning the'recever. The di- I* ode control circuit for the tuning indicator tube is relatively sharplytuned vwith respect to the diode f automatic volumejcontrol circuit andthecontrol i potentialv applied thereto is substantially con- Astant for all signals. l

i Thetuning indicator tubefcomp'rises a target 'i8 which-fluoresces when the tube is energized,

and a shadow isfcast thereon by an electrode 80 connected toan anode-electrode 8| associated withthe control 'gridlii and connected with the sourcel of anode potential'i through a series resistor 8 2. The cperaticnis lsuch that as the. gridl'increases in negative bias in response to automaticvolume control circuit arrangement described,l lies in the fact that by providing aparf allel' channel automatic volume control circuit.

the voltage at the tuning indicator diode issubstantially at or `substantially constant for all y received signals as ldistinguished from the usual circuit in which the voltage may vary fr om one to,30 volts for received input potentialsof from 100 microvolts to one vol `The voltage vdivider circuit provided in the tuning indicator diode output circuit and, in the present example; by the resistor sections 32 'and 33,; aresuch that the proper amountfof rectified voltageI is delivered to `the grid' 'lil` of the tuning indicator tube to give best operation thereof over the ranges of signal strength morefgenerally encountered and the filter means interposed between the voltage divider or diode output circuit impedance and the control gridof the tuning indicator tube, and provided by the series resistorI I3 and v by-pass capacitor 'M are such that the audiofrequency voltage from vthe tuning indicatordiode or signal detector are prevented from reaching'the grid lil.

A further function of the iilter l'i3-JMl is to slow down the action of the tuning indicator tube s ogth'at it will not'be affected by the disturbance ordinarily encountered when tuning i'rornstation to station. The time constant of thisnlter is made large Aenoughjsothat these disturbances do not eiect the tuning indicator tube but is also sufficiently low so that vthe action ofthe tuning indicator tube is not too slow for accurate tuning. y A. i

In uone embodiment of. my invention, the resistor sections 32 and 33 may have a resistance of 56,000 and 220,000 ohms respectively and the resistor i3 may have a resistance of v2.2 megohms with .abyfpass capacitor 'lll of .01 microfarad.

l lead l2 and this is grounded,V as indi-1 cated' at l?, to the chassis and common return decreased," thereby the output resistorsection's `32 and 33, theformer y'that a tap point'l between them 2l as the second'or audio frequency detector may f connection should provideva relatively little or substantially no load upon the diode outputv cir cuit to cause distortion of the audio frequency signals delivered to the audio frequency'amplier- 36.

-With the ,foregoing arrangement, the deection vof the tuning indicator tube is substantially the same for all signals'received and', therefore,

adjustment of the tuning device l2 may be made as accurately for weak stations as for strong ones, since the automatic volume control means operates on a separate channel and provides substantially constantA voltage at the tuningv indicator l vdiode or signal detector.

In receiving sytems wherein a relatively strong signal is developed at the second detector` or at the diode provided for actuating the tuning in dicator device', and particularly if'this diodeY is i utilized as an audio frequency detector the tuning indicator device may be connected through a circuit indicated'in Fig. '2, to which attention is now `directed and in which the same referencefnueA` morals areused for like circuit elements' as in Fig. 1

In Fig. 2, the diode rectifier 2| is provided with f providing a lter vwith the capacitor 35 andthe lead 31 is connected with the tap point 38 for applying audio frequency signals and biasing potentials to the succeeding amplifier tube while I thetuning indicator control lead 12isconnected tothe voltage supply point 38 through a'voltage divider and filter means comprising .a pair of series resistors or resistor sections 85 and 86 connected substantially in shunt with the output resistor 33 for the diode. v Accordingly, such'resi'stor sections' are of relatively high resistance value and, inthe present example, may beof the order of several `Inegohms each and in such ratio with respect to each other is at a lower potential than the point 38, whereby the circuit lead 'i2 receives a relatively low potential suitable for application ofthe control tube indicator device o-r tube. l' l' x A lter capacitor 88 is connected between the lead 'i2 and the low potential side of the diode rectifier circuit substantially in shunt with the resistorA section 86 'which supplies the. control grid of the indicator tube. In one embodiment of the invention the resistor sections 8.5 and 8E when each havey a resistance of 2.2 megohms and the capacitor '88 may have a capacity of .05

" microfarad for ruse with an RCAV6E5 indicator connection therefrom, the capacity of the latter being such that the grid circuit may respond to tuning indications without being subjected 'to' audio frequency potential variations or transient disturbances that might be encountered especially while tuning the receiver.

I claim as my invention:

1. In a radio receiving system, means providing y.

a main tunable signal channel including a signal detector circuit, and an audio frequency amplifier connected therewith, automatic volume control means for said system including a separate signal amplifying channel more broadly responsive to signals than the detector circuit and connected with said first named channel preceding the detector, tuning indicator means having a control grid connected with the said signal detector circuit to receive at least a portion of the vdirect current output voltage therefrom as a biasing potential, and lter means in said grid connection for preventing the audio frequency signal component from being applied to said grid.

2. In a radio receiving system, means provz a main tunable signal channel including a diode signal detector circuit for said system and an audio frequency amplifier connected therewith, automatic volume control means for said system including a separate signal ampliiying channel more broadly responsive to signals than the diode detector circuit and connected with said first named channel preceding the detector, tuning ndicator means having a control grid connected with said diode detector circuit to receive at least a portion of the rectiiied signal output voltage therefrom, and filter nection for preventing the audio frequency signal component from being applied to said grid.

3. A resonance tuning indicator system for radio receiving appar 'tus comprising in coinbination, a main signal amplifying channel sharply responsive to a received signal and terminating in a main signal output circuit for said apparatus, a second signal amplifying channel more broadly responsive to said signal, means for deriving automatic voliune control potentials from said last named channel, and means for deriving a tuning indication from the rst named channel.

4. A resonance tuning indicator system for radio receiving apparatus comprising in ccmbination, a main signal amplifying channel sharply responsive to a received signal and terminating in a main signal output circuit for said apparatus, a second signal amplifying channel more broadly responsive to said signal, means for deriving automatic volume control potentials from said last named channel, means for deriving a direct current potentia1 from the first named channel proportional to the signal strength, and means for deriving a tuning indication from said potential.

5. In a superheterodyne receiver, the combination of variable tuning means, means providing a signal amplifying channel terminating in two separate output circuits, one of which is more broadly responsive to signals than the other, automatic volume control means including a diode rectifier connected with the more broadly responsive circuit and controlling the signal plifying channel, and tuning indicator means cluding a second diode rectilier connected with' the other of said circuits, said last named ineens including a tuning indicator tube having a control grid and a cathode, a diode output resistor in circuit with said last named diode rectiiier and means providing a potential divided tap connection for said control and cathode on said output resistor.

6. In a superheterodyne receiver. the combination of variable tuning means, means providing a signal amplifying channel terminating in two means in said grid con-A Vvolume control means,

cations and audio separate output circuits, one of which is more broadly responsive to signals than the other, automatic volume control means including a diode rectifier connected with the more broadly responsive circuit and tuning indicator means including a second diode rectifier connected with the other of said circuits, said last named means further including a diode output resistor for said diode rectifier, a tuning indicator tube having a control electrode and a cathode connected with said output resistor to receive a control potential therefrom, and a second resistor and by-pass capacitor in said connection providing a timed delay filter for said control grid and isolating 'means between said tube and the output resistor.

7. In a superheterodyne receiver, the combination with tuning control means therefor of a diode second detector, diode automatic volume control means controlling the signal potential applied to said detector, separate intermediate frequency amplifiers for said. detector and automatic volume control means providing differing degrees of selectivity, a diode output resistor for the second detector, a voltage output resistor connected in parallel relation thereto andhaving a relatively high impedance `with respect to said output resistor, automatic volume control circuits connected with said automatic volume control means, and a cathode ray tuning indicator tube having a control grid and a cathode connected with said voltage divider resistor, and an audio frequency lter for the grid connection of said tube.

8. In a radio receiver, the combination with automatic volume control means and the main signal detector of said receiver, of tuned amplifying means for applying signals to said detector, separate and more broadly tuned signal amplifying means for applying signals to said'automatic a tuning indicator device having a control grid connected with the said detector to receiveV control potentials therefrom, and means in said connection providing an audio frequency filter having a predetermined time constant.

9. In a radio receiver, the combination with automatic voume control means and the main signal detector of said receiver, of tuned amplifying means for applying signals to said detector, separate and more broadly tuned signal amplifying means for applying signals to said automatic volume control means, a tuning indicator device having a control grid connected with the said detector to receive control potentials therefrom and said connection further including an audio frequency output frequency output signals are supplied from said diode output resistor.

lf). In a superheterodyne receiver, the combination with tuning control means therefor of a diode second detector. diode automatic volume control means controlling the signal potential applied to said detector, separate intermediate fre-- quency amplifiers for said detector and automatic volume control means providing differing degrees of selectivity, a diode output resistor for the second detector, automatic volume control circuits connected with said automatic volume control means, and a cathode ray tuning indicator tube having a lcontrol grid and a cathode connected with said resistor, and an audio frequency filter for the grid connection of said tube.

FRED B. STONE.

circuit whereby tuning inditill 

